1. Field of the Invention
The present invention relates to a composite rope suitable for use as the material for reinforcing concrete structures, the rope for holding various equipments on boats and ships and anchoring boats and ships themselves, the material for reinforcing cables not to become loose, the cable for operating cars and air planes, and the material for reinforcing non-magnetic structures. The present invention also relates to a method of manufacturing the composite rope.
2. Description of the Related Art
Japanese Patent Publication Sho 57-25679 discloses a technique of impregnating multifilaments, high tensile strength and low elongation, with a thermo setting resin to prepare a corrosion-resistant composite rope, substantially same in strength and elongation but lighter, as compared with the conventional wire rope.
According to this technique, the multifilaments, high in strength but low in extension, are twisted together, in such a way that their strength-utilizing efficiency becomes higher than 50%, to prepare a primarily-twisted product (e.g. yarn of continuous fiber). The term "strength-utilizing efficiency .eta." means a ratio between the tensile strength of a bundle of the multifilaments not twisted and that of the bundle of them twisted. The primarily-twisted product is impregnated with a thermosetting resin, which has been so set as to hold the primarily-twisted product as it is, and then coated at the outer circumference thereof with a thermoplastic resin. Plural products thus formed are twisted or laid together to prepare a secondarily-twisted product (e.g. cable). This secondarily-twisted or -laid product is heated to set the impregnated resin and to provide a composite rope.
The reason why the primarily-twisted product is coated with thermoplastic resin resides in enhancing the forming ability of the composite rope and protecting the rope.
According to the above-described technique, the primarily-twisted product is impregnated with thermosetting resin and then coated at the outer circumference with thermoplastic resin. Therefore, the coating resin makes the inside of the primarily-twisted product air-tight, causing air to be caught in it in the course of impregnating and coating it with resins. Further, volatile gas caused when the thermosetting resin is heated and a part of solvent in the resin are caught and left in it. These air, gas and solvent are present as voids in it, causing the composite rope, which is the final product, to become low in mechanical property.
U.S. Pat. No. 4,677,818 discloses another technique of eliminating the above-mentioned drawbacks to prepare a composite rope, higher in strength and lower in extension.
According to this second technique, the primarily-twisted product which has been impregnated with resin is attached by smoothing powder (or talc) and further wrapped at the outer circumference thereof by a woven fabric (cloth). And the primarily-twisted product thus wrapped by the cloth is heated to set the impregnating resin. Air, gas and solvent caught in the primarily-twisted product can be thus escaped through meshes of the cloth, thereby enabling no void to be left in the primarily-twisted product.
However, the cloth is formed by fibers woven together. Therefore, the thickness of the cloth wrapped round the primarily-twisted product becomes theoretically two times the diameter of the fiber woven and it sometimes reaches 0.5 mm in the thickest. When the primarily-twisted product is wrapped by the cloth, therefore, its diameter becomes large and this makes it impossible to prepare a compact composite rope.